An OLED is a novel flat panel display device, which has many advantages of actively emitting lights, and having a high brightness, ultra thinness, low power consumption, wide viewing angle, wide range of working temperatures, and the like.
The OLED is a multi-layer thin film laminated structure, in which several organic material layers are sandwiched between a pair of electrodes. When an appropriate voltage is applied, electrons and holes are injected from the corresponding electrodes into the organic material layers, and the electrons and the holes are encountered and captured at corresponding positions during transmission, release energies, and emit lights. A total thickness of the multi-layer thin film laminated structure is usually several micrometers or even smaller, such that the OLED is usually manufactured on a substrate with a certain thickness. The commonly adopted substrate is glass, and when a bottom electrode is a transparent material, light rays may be emitted from the substrate on the side of the bottom electrode, and in this case, a light transmission ratio of a top electrode is not urgently required.
When the OLED is utilized in the displaying application, in one structure, several device units are arranged as a display screen having a matrix structure, in which positive electrodes of each column are connected, and negative electrodes of each row are connected, so as to achieve a dynamic displaying effect through row scanning and column scanning. The OLED is a current-type device, and the brightness thereof nearly has a linear relation with the current. It is assumed that a driving signal scans from left to right, when a bottom right end on the screen intends to obtain the brightness the same as that of a top left end on the screen, the bottom right end needs a much larger voltage. Thus, as for a display screen having hundreds of rows and columns, it is difficult for such a display screen structure to realize a high-resolution displaying effect.
Therefore, in the prior art, another display screen adopting thin film transistors (TFTs) is proposed. The TFT is disposed in each pixel unit to control ON/OFF of the current, and a current (line) layer having a sufficient small resistance is disposed, such that each pixel in the display screen is enabled to obtain the same driving current, thereby realizing the high-resolution displaying effect. However, the TFTs in the display screen with such a structure occupy a large part of the projection area of the pixel units, and the TFTs have a quite low light transmission ratio and are almost opaque, such that the light transmission ratio of the display screen with such a structure is rather low, and has a low aperture ratio. Although the aperture ratio of the display screen may be appropriately increased by reducing an area of the TFTs, an area of the pixel units is quite small, such that the reduction of the area of the TFTs further increases the difficulty in the manufacturing technique.